Gardening Tips: Greenhouses

Editor’s Note: We’ve been reaching into Michelle Smith’s archive to present always timely gardening advice. This week’s column first appeared on 31 May 2017.

Editor’s Second Note: We are delighted to have Michelle Smith back with us this week, elsewhere in this edition!


What to do this week

Managing your greenhouse may be on your mind this week. Hopefully people who do have greenhouses have things in there by now. But if you haven’t moved things out, it is time to start doing it.

Things like your onion transplants should all be in your greenhouse. They can actually even take a little bit of frost. Tomato plants —  and the warm season stuff like peppers and eggplants and basil — will not necessarily be damaged in the greenhouse over night, but you might want to help them out a bit when it’s very cool. They can’t really manage well below 10 degrees Celsius. Tomatoes could get blight. So it may be best not to move things to the greenhouse if it is still very cool. But if we have had a run of warm weather, and you have to move things out of your house, there are things you can do to prevent problems.

By Jürgi-würgi (Own work) [Public domain], via Wikimedia Commons

Greenhouse (Photo By Jürgi-würgi, own work, Public Domain, via Wikimedia Commons)

I don’t have a heated greenhouse. It is expensive and not a great use of fossil fuels, but I do put a heat lamp in if it seems to be needed, and just put it on at night. I might have even done that for the onions and the brassicas a few weeks ago. Now I wouldn’t bother for them, but for tomatoes and other warm season plants, I would do it on a cool night. I know they will likely not freeze in the greenhouse, but I don’t want them to get cold stressed.

There are other things you can do to make your greenhouse or cold frame more friendly in this weather. Glass or plastic or whatever the material in your greenhouse does not hold the heat. You may find it quite warm during the day, but this temperature drops very quickly at night. If you can slow that cycle down a bit, if you can keep some of that daytime heat from dissipating so quickly, that is really the best situation. If your greenhouse is big enough, you can do what I do. I use 45 gallon barrels and fill them with water. That water will warm up during the day, but it will release this heat slowly. You can sometimes get quite a few degrees of temperature moderation from this. You can even put a plank over these two barrels and have an additional working space. If your space is smaller, you can add big rocks here and there, or even as many plastic milk jugs filled with water as you can fit. You can paint them black, but you don’t have to. You just want something to add thermal mass to your greenhouse.

The greenhouse protects plants from UV and wind shock, so aside from the coolness at night you don’t have to worry about gradually introducing your plants to the greenhouse. But when it is time to move plants out into the elements, from the greenhouse or from your house, you have to harden them off gradually. Next week I will talk about hardening off your plants.
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Market gardener, farmer, workshop leader, seed-saver, political candidate and mother, Michelle Smith has spent over 30 years coping with the challenges of our bioregion and in the process has built a store of practical and technical knowledge. The Inverness resident has served on the board of Seeds of Diversity Canada and represented Alternative Producers with the Federation of Agriculture but can do nothing about her hair. She is pictured with a head of Club Wheat, a seed that shares her approach to hairdressing.



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